Manufacture of nitric acid



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MANUFACTURE OF NITRIC ACID Filed `(not. 29. 1921 .NUJOOU MOH., PMAFDO Moz Mom mmJOou moz: uom EJkao NQkdNDv/Imo 50mm vowNI Patented July 12,1927. y l

UNITED STATES` PATENT OFFICE..

EDWIN L. NELLIS, OF ALLENTOWN, PENNSYLVANIA, ASSIGNOR- TO TROJAN POWDER COMPANY, or NEW YORK, N. Y.,

A GORYORATION OF NEW YORK.

MANUFACTURE OF NITRIC ACID.

Application filed October 29, 1921. Serial No. 511,264.

This invention relates to improveinents in the manufacture of nitric acid.

In the usual process of making nitric acid, sodium nitrate and sulfuric acid are heated together in a retort, and the distillate is condensed. This vdistillate varies incomposition at different periods during the time of heating, the first and last portions of the dis- `tillate from ea'ch run being relatively weak,

while the main quantity of the distillate is approximately 97% HNO3. This weakness of the first and latter portions of the distillate is due to the water introduced into the ret-ort with thenitrate of soda and with the sulfuric acid, this water passing over and diluting the nitric acidi of the distillate. The amount of water in the nitric acid as it distills over varies with the amount of water introduced into the retort with the nitrate of soda and the sulfuric acid and with the intensity of the fire under the retort, and also to a great extent with the amount of the sulfuric acid, an excess of sulfuricacid having a tendency to hold the waterland pre- 1 vent its going over into the condenser with the nitric acid. i

In the usual process, the weak and the strong acids produced arecollected into sepa-- rate containers, the amount of strong acid varying from 75% to 90% of the total output and varying in strength from 85%' nitriclacid to 93% nitric acid, depending largely` upon the amount of `sulfuric acid used for charging the retort and upon the length` of the distillation. The weak nitric acid comprising approximately 8% to 25% of the total production, is either put back into the retort with the nextV charge of sul- `furie acid or put through a special process low in nitric aci I In carrying out my? process, a charge of nitrate of soda is placed 1n a still, and there il added tothis nitrate of sode apJ proximately three-fourths of the amount of sulfuric acid which is to be used in the run. The distillation is then commenced by heat ing the still, and soon acid begins to come over. As previously stated, this first distillate is not very strong, and some of the sulfuric acid held in reserve is allowed to trickle in countercurrent to the uprising vae pors to dehydrate them. As the distillation continues, the acid coming over becomes rapidly stronger, and as soon as it reaches the desired predetermined strength, the flow of the dehydrating acid is shut off. For some time the acid continues to come over at the given strength, but toward the end of the distillation it begins again to lack strength. The dehydrating acid is now again started and continues to run until the entire reserve amount has run into the still. As

soon as all the dehydrating acid has been used up, the nitric acid coming from the still begins to drop in strength, and as soon as the strength drops below the predetermined percentage, this weaker Vacidis col-A lected separately. The distillation of the weak acid is continued until the acid distilling over drops in strength to a predetermined point, when the fire is pulled from under the still. All of this dilute acid is gathered together and is mixed with thrcefourths of the amount of sulfuric acid constituting the acid charge for t-he nest run, and the entire operation is repeated.

In the attached drawing, I have illustrated diagrammatically apparatus for carrying t out my process. In this drawing, l ,indicates a tank for the sulfuric acid used in charging the retort 2, withwhich retort the tank is connected by means of a pipe line 8. 4 represents the dehydrator comprising a suitable casing which is packed or filled with quartz ranging in size from .six inches in diarneter at the bottom to two inches in diameter at the top of the packing, this dehydrator having at the bottom an intake opening connected with the retort by means of a coiled duct and being connected at the top by means of a duct 6 with a tank 7 containing sulfuric acid. The arrangement is such that the distillate passing from the retort through the duct 5 passes upwardly through the quartz filling toward the exhaust duct 8 leading from the top of the dehydrator, sulfuric acid at the sameftime being introduced in the top of the distributor from ceV M it

the tank 7, the flow of the acid being broken up by the quartz filling of the dehydrator and presenting a large surface of sulfuric acid to the upcoming nitric gases. The duct 8 communicates with a blcacher 9 of the usual Well known construction, which performs the same function as the bleacher in other forms of nitric acid plants, the gases passing from the bleacher to the condenser 10, where they are condensed, the condensed acid flowing back through the condenser, countercurrent to the flott.T of the gases, then into the top of the bleacher9 Where it also flows countercurrent to the hot gases passing' up through the bleachcr V9. From the bleacher 9, the condensed nitric acid flows out through the trap and into the cooler, both shown in the print. An outlet is provided in the cooler Where the nitric acid may be drawn into the container. The dehydrating acid is led from the bottom of the dehydra'tor through a pipe line 11 to the retort Where it functions with the remainder of the acid charge in decomposing the sodium nitrate.

As a specific example of my process, l may charge the retort With any desired amount, within its capacity, of nitrate of lsoda, to which is added, as previously described. thresfourths of the amount of sulfuric acid which is to be used in the run, this acid being int-roduced from the tanlt 1. Since the ratio of nitrate of soda to sulfuric acid for the 'entire run is 1 to 1.05, l place in the still 787% lbs. of 100% sulfuric acid (as 90% acid) for each 1000 lbs. of 100% nitrate of soda, and l hold in reserve one-fourth of the amount of the sulfuric acid to be eniployed, :mounting to 202% lbs. of 100% sulfuric acid 90% acid). As indicated, acid of 96% strength is the actual acid used, the amount of tho 90% acid being 820.3 lbs. The distillation is then commenced by heating` the still, and soon' acid begins to come over. This acid is not very strong, and accordingly some of the 2621/2 lbs. of reserve sulfuric acid which is held in the tanlr 7 is allowed to triclrle in countercurrent to the uprising vapors in the dehydrator, the amount of sulfuric acid so used being approximatelyv tivo lbs. per minute for each 1000 lbs. of sodium nitrate charged in the still., but varying somewhat with the strength of the nitric. acid being made as determined by samples and tests made during the distillation. As soon as the acid coming over from the still reaches 97% in strength, the iioiv of dehydrating acid is shut olf and the distillation is continued in this fashion until toward the end of the distillation the nitric acid distillate begins again to weaken. Atthis point, the dehydrating acid again is started and continues to, run until all, ofthe 2021/2 lbs. of reserve have run into the still, at lwhich ypoint the nitric acid comingfrom the still beginsI to drop in strength. As soon as the strength drops below 97%, the subsequent weaker acid is collected separately, the distillation of the Weak acid continuing until the acid distilling over drops to about degrees B. in strength (41% HNOS). The tire is then pulled from under the still, the heat of the retort still causing some distillation to go on, however, and all of this dilute acid is gathered together and mixed With the initial charge of sulfuricl acid for the next run.

The complete operation therefore consists in charging into a retort an amount of nitrate of soca, adding to this nitrate of soda substantially three-fourths of its Weight of sulfuric acid, to which is mixed the dilute ends from the preceding distillation, and then distilling, the distillate Whenever below 97% being run countercurrent to adtitional sulfuric acid until an additional amount of sulfuric acid equal to one-fourth of the weight of soda charged has been used up and hasentered the retort. The distillate thereafter is considered as ends, and is added to the sulfuric acid in the next following run.

In the usual method of manufacturing hereinbefore described, the amount of strong acid obtained Will vary from to 92% of the total output, and will vary in strength from ,nitric acid to 93% nitric acid, depending on the amount of sulfuric acid used for charging the retort and upon the length of the distillation. According to the present invention, using the apparatus described, to 93% ot' the total nitric acid made is of 97%` strength, While 7% to 10% is Weak, averaging 75% nitric acid. 1t will be noted that this Weal; nitric acid is put bach into the retort for the next distillation with no excess of sulfuric acid over and above that previously employed as the initial acid charge, that by this method the total output of nitric acid is produced at a strength of 97%, with the 'use of one lb. of nitrate of soda of 100% Vstrength to 1.05 lbs. of 100% sulfuric acid as 90% strength.

As pointed out, my process .shows substantial economies in operation, and as a further advantage, the Water which otherwise ivould appear in the nitric acid distillate remains` in the still with the sodium acid sulfate or niter cale left afterv distillation, this .uiter cal e accordingly containing a higher percentage of Water than niter cake made in accordance with customary procedure. Under these conditions, the niter cake is more fluid and is more readily. removed from the still.

I claim:

1. In the manufact-ure of nitric acid by distillation ofreaction products of nitrate of soda ivit-h sulfuric acid, the process which comprises reserving approximately onelili) fourth of the total amount of sulfuric acid used in a distillation, and passing said reserve acid int-o the still in countercurrent to the weak distillate.

2. In the manufacture of nitric acid by distillation of reaction products of nitratev of soda with sulfuric acid, the process which comprises passing sulfuric acid prior to its participation in the reaction in countercurrent to the distillate running less than 97 nitric acid at such a rate that the resulting distillate Will contain not less than 97% nitric acid.

3. In the manufacture of nitric acid by distillation of reaction products of nitrate of soda with sulfuric acid, the process Which comprises reserving approximately onefourth of the entire quantity of sulfuric acid used in said reaction, and passing said reserve acid prior to its participation in the reaction in countercurrent to that portion of the distillate containing less than 97 nitric acid and at such a rate that the result-- ing distillate is brought to 97 nitric acid.

4.. In the manufacture of nitric acid by distillation of reaction products of nitrate of soda with sulfuric acid, the process which comprises starting the diffillation of the nitrate' of soda With subsntially threefourths of its Weight of suliuric acid, and passing a quantity of sulfuric acid approximately equal to one-fourth the Weight of soda into the still in countercurrent to those portions of the distillate running below 97% nitric acid and at such a rate that the said portions of the distillate are brought to 97% nitric acid.

5. In the manufacture of nitric acid by distillation of reaction products of nitrate of soda with sulfuric acid, the process Which comprises starting the distillation of the nitrate of soda With substantially threefourths of its Weight of sulfuric acid, passing a quantity of sulfuric acid approximately equal to one-fourth the Weight of soda into the still in counter-current to those portions of the distillate running below 97% nitric acid and at Such a rate that said portions are brought to 97% nitric acid, collecting the distillate falling in strength below 97% nitric acid following exhaustion of the strengthening acid, and adding the Weak distillate to the sulfuric acid employed in the next following distillation.

6. In the manufacture of nitric acid by distillation of reaction products of nitrate of soda and sulfuric acid, the process which comprises reserving of the sulfuric acid employed in the reaction, running the reserve acid in countercurrent to portions of the distillate falling' in strength below 97% nitric acid and at such a rate that the resulting distillate Will contain 97% of nitric acid, collecting those portions of the distillate following exhaustion of the reserve acid which fall below 97 and adding this collected distillate to the sulfuric acid employed in the next run.

7. In the .manufacture of nitric acid by distillation of reaction products of nitrate of soda and sulfuric acid, the process which comprises reserving approximately onefourth of the sulfuric acid employed in said reaction, passing the reserve acid in countercurrent to portions of the distillate running less than. 97 nitric acid at such a rate that this Weak distillate is brought to 97 nitric acid, collecting the distillate passing over after the exhaustion of the reserve acid which contains less than 97% nitric acid, and adding this latter portion of the distillate to the said reserve sulfuric acid employed in the next run.

EDWIN L. NELLIS. 

